In the biophysics of membrane processes, there is a wide current interest in the possibility that membrane constituents undergo molecular orientation and conformational changes during membrane function, and that many membranes consist of mosaics, some parts of which are fluid. Among the forces which relate to orientation and conformation changes, the transmembrane electric field acting on dipolar membrane constituents is of particular interest. However, there appears to be no data on polarization effects in appropriate two-dimensional analogous structures, on which to base quantitative arguments as to the relevance and magnitude of such effects in biomembranes. Following recent advances in the thermodynamics of electric field effects at liquid surfaces containing monolayers, it is known that in addition to orientation and conformational effects, fields may also induce composition and pressure changes and modifiy phase behavior in surfaces. This thermodynamic analysis has been extended in the current program to the behavior of dielectric layers between metal electrodes, and is capable of being further extended to black lipid film systems. Certain effects predicted by this thermodynamic analysis have not been observed hitherto. After one year of the current project, the qualitative effect of field on the first order phase transition of pentadecylic acid has now been demonstrated, and the remaining year will be required to quantitate the phenomenon and to demonstrate field-induced surface pressure changes in dense monolayers. The extension is sought to move on to other predicted field-dependent phenomena in systems closer to biomembranes, namely the effect of fields on the local composition of multicomponent monolayers, on the adsorptoion of ions, and on higher order phase transitions in pure or multicomponent monolayers.